The first thing Foster does, on alighting from his chauffered Range Rover outside the Gherkin, is to turn you round and point out the deficiencies of the opposition. There is Tower 42, still known to many as the NatWest Tower, which until the Canary Wharf complex out east in the former Docklands came along was Britain's tallest. At 590 feet the Gherkin is fractionally shorter than that but, as Foster points out, you can't get anywhere near the top of Tower 42 - there's just a great big lump of leftover concrete and equipment stuck up there. Foster does not mention the nearby Lloyd's of London building by his old friend and Sixties business partner Lord (Richard) Rogers, which with all its metal pipes and lumps and bumps divides opinion far more than the Gherkin. The Lloyd's building is as Gothically rambling as the Gherkin is classically, symmetrically, pure. And it's not a skyscraper. But you get great, diamond-framed views of it from inside Foster's building. The yin and the yang of the style once known as high-tech, divided along ancient and immutable architectural desire lines, here engage in a fruitful conversation.

Foster then spins back round and faces his own building. Point taken. That curving, slippery shape, tapering towards the bottom as well as the top, seems to occupy less space than its rival towers. Your line of vision, like the wind, slides round it rather than bouncing off it. Foster could have filled his site right up to the pavement, but chose to go tall instead. The consequence is that there is space for a new city square at the base, with seats and, soon, shops and cafes. And of course the fortunate few can go right to the top and see all round or even vertically upwards: there is a circular domed skylight right in its nosecone. This happens to be the only curved piece of glass in the whole building.